


The Irregular at Fuyuki High

by RedGrammar



Category: Fate/stay night & Related Fandoms, Fate/stay night (Visual Novel), 魔法科高校の劣等生 | Mahouka Koukou no Rettousei | The Irregular at Magic High School
Genre: Crossover, Implied/Referenced Incest
Language: English
Status: Completed
Published: 2018-02-27
Updated: 2018-02-27
Packaged: 2019-03-24 15:14:49
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 2,154
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13813842
Author URL: https://archiveofourown.org/users/RedGrammar/pseuds/RedGrammar
Summary: Cornered by a strange magic entity called a servant, Emiya Shirou summons a servant of his own, a mage by the name of Shiba Tatsuya who proceeds to show the Fuyuki Holy Grail War how Oniisama handles things.





	The Irregular at Fuyuki High

Emiya Shirou dragged himself across his shed, trying to dodge Lancer's sharp stabs, but quickly found himself cornered. As Lancer prepared to finish off the teenager, a bright blue flash erupted out of the ground and threw Lancer outside.  
Back against the wall, hand holding a gaping wound, Shirou looked up. A young man in a white uniform with neat black hair and very handsome features looked down on him. 

"I am confirming the situation, but are you my master?"  
"huh, what master?"  
"No, it is nothing, we'll speak later."  
In that short nano-second, the summoned man had used his analytical eyes to see the flow of mana around the injured man and his analytical brain, that had traded all emotions for superior computing abilities, quickly deduced that the young boy in front of him was not a seasoned mage. It was an incredible deduction that only he could make in such a short amount of time. Truly remarkable.

As Shiba Tatsuya eyed his opponent, his analytical mind once more kicked in and he quickly deduced from the large red spear his opponent was holding that his opponent was of the Lancer class. Once more, it was a remarkable deduction only he could make.

This was an unwelcome matchup. Unwelcome not because Shiba Tatsuya had any weaknesses or enemies he could not defeat, but because the Lancer class was prone to self-destruction and thus Tatsuya would not be able to demonstrate the full extent of his abilities.

Not that Shiba Tatsuya wanted to showoff or anything of course. He did not mind if the enemy was easily defeated. If anything he preferred to keep the extent of his abilities a secret, but what a shame! The world should know of how incredible he was. 

Shirou grabbed his throbbing head. What was that? Shortly after he had looked at this 'Tatsuya', a verbal vomit of exposition spoken by a reasonably high pitched girl had overloaded his mind. Who was this Tatsuya? Did he have a fangirl, or a fanclub, following him wherever he went? 

"You, who are you?" Lancer yelled at Tatsuya.  
Tatsuya stepped out of the room and answered "just a weed".  
"Huh, what the heck is a weed? I sense mana, so you are a mage? A Caster huh?"  
"No, I am a terrible mage who wouldn't be selected for the Caster class."

The head throbbing came back as the voice in Shirou's head loudly proclaimed "NO THAT IS NOT TRUE. HE IS THE STRONGEST MAGICIAN. It is just the test for magic, both in our world and this one, can't assess his true strength! He is an irregular!"

As Lancer prepared to strike again, Tatsuya quickly activated his CAD and brought forth a GUN which he proceeded to use to fire blue magic bolts at Lancer. 

Lancer deftly dodged the shots before speaking up once more, "huh a gun, so you're an Archer". 

"No," Tatsuya kept his gun poised and firing, "I am not an Archer. I am a Saber."  
"Huh!?" Lancer exclaimed before having to hastily dodge another shot, "you are a Saber?!"  
"Indeed. My entire body is a weapon thus I am a Saber."  
"Ridiculous, that is impossible!"

Suddenly Shirou's head pain came back far more viciously than it had ever before and the internal voice very loudly proclaimed "ONIISAMA MAKING THE IMPOSSIBLE POSSIBLE!".

Shirou almost collapsed from the yell, but the pain quickly subsided and Lancer, fed up with this strange opponent, retreated. 

"Are you all right?" Tatsuya asked as he turned to Shirou.  
"Yeah umm Tatsuya?"  
"Yes, that is my name and you are?"  
"Emiya Shirou and I have no idea what is going on here."

Despite the constant droning of the voice in his head, Emiya Shirou understood nothing about his current circumstances. He felt he knew far more about the man in front of him then he ever needed to know, but why he was here, what a Lancer was, what a Saber was, all of these questions were ignored by the exposition playing out during the fight. 

Just then Tatsuya turned around and brought out his gun again. Another master servant pair had suddenly shown up.

"Heh to think you became a Master too Emiya Shirou" Tohsaka Rin said. 

Noting the apparent friendship between his Master and the black haired girl, Tatsuya relaxed his arm, but kept his finger on the trigger. Tatsuya, the rational being that he was, understood all too well the fickle nature of friendships. 

Of course no friend of Tatsuya would ever betray him because it was obvious to them betrayal would never work in their favor, but betrayals by friends of other, less reliable people like his master, were more than possible.

Before Shirou could reply to Tohsaka he felt a great confusion in his mind as the mysterious voice wondered how any girl could ignore Oniisama for another man. Bizarre. This girl was likely not trustworthy. Then again, less rivals were perhaps a good thing, no it was absolutely not. Everyone must come to understand Oniisama's charm.

Tohsaka Rin explained the situation to Emiya and the four of them decided to go the church and meet the overseer. Tatsuya waited outside as Rin and Shirou met the supervisor. Archer eyed Tatsuya and thought about opening a philosophical dialogue with the fellow servant, but Tatsuya's strong pose left no room for debate. This was a man set in his ways, preaching to him was useless. Archer sighed, acknowledging the fellow servant's superior brooding abilities.

As Shirou was about to leave, Kotomine called out to him. "Shonen, I do not know why the Grail give you who it did, but your servant's ideals are far different than your own. Best of luck."

"Saber. I am willing to fight in this Holy Grail. Do you want to know what we talked about?" Shirou asked his servant as they walked back.  
"No, it is fine. In fact we have something else we must deal with." Tatsuya said nodding to the silver haired girl who had showed up.

"Good evening Oniisan" the girl said curtsying.  
"WHAT," the voice in Shirou's voice rung out in anguish. Once more a girl was addressing this carrot boy before Oniisama. Did the people of this world have no clue about how to discern and respect true talent? Frustrating!"

"Ugh," Shirou clasped his head in pain and when he opened his eyes once more, Tatsuya had disappeared and half a nanosecond later appeared behind Illya holding a gun to her head. Shocked, Illya loudly proclaimed, "impossible! my barrier." 

"ONIISAMA MAKING THE IMPOSS-" Shirou immediately slapped a picture of a majestic sword into his head to cut out the intrusive voice. 

Noting the great power and ability of the large Berserker class servant, Tatsuya had immediately recalled his training, "if the terrorists have a big gun, aim for the terrorist not the gun".  
"SABER STOP!" Shirou yelled out, accidentally activating the command seal. Unfortunately, or fortunately because Shiba Tatsuya never made the wrong decision, the seal reversed the command. Immediately upon being summoned Tatsuya had reverse engineered the Holy Grail system and rewritten it to rebound if he were given a command. Shirou collapsed on his knee, holding his throbbing hand. 

Tatsuya was about to eliminate Illya, but unlike the weapons his enemies used, servants had a fair bit of autonomy, so the Berserker took a swipe at Tatsuya who nimbly stepped back, abandoning his combat maneuver. 

Tired with the entire affair, Illya left them alone but not before telling Shirou his servant was really boring and she had expected someone more fun.

Tatsuya began to regroup mentally as he accompanied his master home. Shirou was babling about how Tatsuya shouldn't attack young girls, but his words fell on deaf ears as anyone who came between Tatsuya and his goal was to be eliminated. His goal....what was his goal here? During life Tatsuya's only goal was the betterment of his sister, but now she wasn't here anymore. What was he even fighting for? 

A calculation that would have taken ordinary humans weeks was done in half a second in Tatsuya's super brain. He knew now exactly what he was fighting for, his sister, Miyuki. She wasn't here of course, but with the grail he could summon her here and they could live together, free of their many enemies and their constant desire for magic equality. Yes, that's what he would do from now on. Some preparations to win the war would be required and Tatsuya spent the night thinking about how to fight this war.

The next day as Shirou walked to class, he noticed an old lady struggling to cross the street. Shirou immediately offered her his shoulder and helped her cross the street. A bit later he found someone else struggling to climb the stairs and once more he lent them his back and helped them to the top of the pedestrian bridge. Accompanying Shirou in spirit form, Tatsuya watched these exchanges and more with disgust. Later in the day when Shirou was helping clean the archery club during lunch, Tatsuya materialized and asked him, "why do you help others?"  
"Excuse me?"  
"Earlier today you helped several people walk and now you lend your services to a club you are not part of."  
"Well, it is just the way I a-"  
"It is not acceptable. You can't help people cross the street. Now they will always expect help."  
"what?"  
"It is simple logic. If you simply help those who claim to be in need, they will never learn to help themselves. We worked hard to learn how to cross the street on our legs, why should we help those not willing to take the time to learn?"  
Shirou sighed and ignored Tatsuya. This servant was stupid. He was unbelievably stupid. "To summon a servant even dumber than you, that sure is impressive" Rin would later tell Shirou over dinner.

The next day as he was walking to school, Shirou felt Tatsuya tap him on the shoulder. "Emiya, I have thought about our upcoming battles and have come to a battle plan that will maximize success."  
"Um, that's good and all but why are you telling me this now, in public."  
Tatsuya pointed to a shop across the street.  
"We need to procure some items for this plan."  
Shirou was really confused, but Tatsuya had a determined look in his eyes, so he decided to go along with this plan.  
\--------------------------------------

Tatsuya's magic shot was reflected with ease by Kuzuki's magic enhanced fists who moved in close and pushed Tatsuya back.  
"EMIYA NOW!"  
"eh, do I really have to" Shirou said, more than a little embarrassed.  
"Yes, it is the only way we can win" a (slightly) exasperated Tatsuya replied. 

Shirou sighed and shyly reached out into his bag. He pulled out a wig. A dark blue wig.  
"NOW MASTER" Tatsuya yelled.  
Shirou slowly put on the long hair. Caster's heart began to race and her face took on a blush as she thought of outfits that would suit this boy.  
"G-o g-g-o do your best!" Shirou said weakly.  
"More enthusiasm!" his servant yelled back  
Shirou closed his eyes, handing himself over to the voice in his head and proceeded to yell at the top of their voice "ONIISAMA YOU CAN WIN THIS!".

"AAAAAAHHHH" spurred by his sister's enthusiasm, Tatsuya activated his most advanced cad, broke the magic construction of Caster's spells and began to push back her master. The Caster pair retreated (Caster still sad she couldn't dress up Shirou) and Tatsuya turned around. Standing there, waiting for him was his younger sister. She was the sole reason for his existence.

"Oniisama," Miyuki whispered as Tatsuya placed his hand on her face. It had been so long since he had seen her. If he still had emotions he would cry. Miyuki reached for Tatsuya's hand with her own,  
"Oniisama"  
"Miyuk-" Tatsuya stopped. His keen eyes had noticed a discrepancy and his sharp brain immediately sprung into action. Beneath the blue hair, barely visible against the forehead, was wig netting. Tatsuya turned around, dismayed. His hand clenched into a fist.  
This wasn't his sister. This was Emiya Shirou disguised as Miyuki to bring out Tatsuya's latent abilities. Tatsuya's fist tightened. He would win this Holy Grail War and wish for his sister. Nothing would get in his way.

Wearing a very weary expression, Emiya reached for, pulled down the wig and looked at his servant. This man, Tatsuya, was an idiot and incredibly tough to handle. Shirou was not sure what would happen and whether both of them would die a quick death reaching for a grail Shirou had no real wish for. Shirou sighed. Still, as the sun set and highlighted the back silhouette of his servant, Shirou noted, his servant may have had nothing going for him personality wise, but he sure had a mighty fine ass.


End file.
